tools/gen_presets: build into cmake-build-<board> with single-config Ninja

Change the default configure preset binaryDir from build/<board> to
cmake-build-<board> (the dir name HIL expects) and switch the generator
from Ninja Multi-Config to single-config Ninja. Multi-Config nests
binaries under a RelWithDebInfo/ subdir, which hil_test.py does not look
in; single-config emits device/<ex>/<ex>.elf so preset-built firmware is
directly consumable by `hil_test.py -B examples`.

Regenerated BoardPresets.json (also picks up the tracked ch32v103c_bluepill
board that was missing from presets).

Co-Authored-By: Claude Opus 4.8 (1M context) <noreply@anthropic.com>